Copper film forming method and manufacturing method of multi-layer wiring substrate

ABSTRACT

A copper film forming method including the steps of spraying a copper formate solution including a copper foramate and a solvent which is evaporated at a certain temperature on a surface of the substrate, and spraying a reducing agent solution including a reducing agent for reducing a copper oxide or undecomposed copper formate on the surface of the substrate to the surface of the substrate. The spraying steps are performed while heating the substrate to the certain temperature and the substrate is placed in an inert gas which is inert at the certain temperature.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a copper film forming method and manufacturing method of a multi-layer wiring substrate using the copper film formation method. More specifically, it pertains to a copper film forming method for forming a thin copper film on a surface of a substrate.

2. Description of Related Art

In order to form a certain pattern on one side of a substrate, it is the common practice to form a copper film on the entire surface on the one side of the substrate by electroless copper plating.

Such electroless copper plating inevitably uses a harmful substance such as formaldehyde. Therefore, a cumbersome treatment is necessary for the treatment of a waste liquid left after electroless copper plating.

Thus, process of thermally decomposing copper formate, thereby forming a copper film are proposed as a process capable of forming a copper film on one side of a substrate without using such electroless copper plating.

For example, Japanese Patent Unexamined JP-A-11-193461 proposes a process of thermally decomposing copper formate in a pressure-reduced atmosphere, thereby precipitating copper on one side of a polyimide film.

Further, Japanese Patent Unexamined Publication JP-A-2002-271000 proposes a process of forming a copper interconnect by applying and drying a copper formate solution on one side of a substrate and exposing the substrate to laser light to precipitate copper.

Still Further, Japanese Patent Unexamined Publication JP-A-06-93455 proposes a process of forming a copper film by thermally decomposing copper formate on the surface of a base material in the presence of palladium.

Furthermore, Japanese Patent Unexamined Publication JP-A-2005-35984 proposes a process of forming a copper film on the surface of a base material by placing a copper compound represented by the formula: [RCOO]_(m)[NH₃]_(n)CuX_(p) (wherein, m is from 1 to 3, n is from 1 to 3, and p is from 0 to 1) on the surface of a base material and heating the base material under a copper non-oxidizing atmosphere.

According to the above-described patent documents, a copper film can be formed on a surface of a substrate without employing electroless copper plating and therefore cumbersome waste treatment of an electroless copper plating solution can be omitted.

However, in the JP-A-11-193461 and JP-A-2002-271000, a copper film is formed by thermally decomposing powdery copper formate over a substrate. During thermal decomposition of copper formate, a copper film becomes porous due to emission of a thermal decomposition gas such as carbon dioxide gas. To provide a copper film with enough conductivity, the thickness of the film must be increased to about 2 μm.

Accordingly, the processes according to the JP-A-11-193461 and JP-A-2002-271000 have difficulty in forming a copper film as thin as 1 μm or less and at the same time, having enough conductivity.

Compared with these processes, the process disclosed in the JP-A-06-93455 uses expensive palladium, which raises a film formation cost. In addition, a dispersed state of palladium on the surface of the base material has an influence on the purity and the like of the copper film thus formed. It is therefore very hard to form a uniform copper film.

In the JP-A-2005-35984, the copper compound represented by the formula: [RCOO]_(m)[NH₃]_(n)CuX_(p) is not commercially available and must be synthesized so that a formation cost of a copper film becomes high. In addition, the copper compound thermally decomposes at a relatively low temperature even in the absence of a catalyst so that it is likely to be influenced by whether or not the atmospheric temperature during heating is uniform. A uniform copper film on the surface of a base material is therefore difficult.

SUMMARY OF THE INVENTION

An object of the present invention is therefore to overcome the problem of the above copper film formation method employing thermal decomposition of copper formate or a compound thereof, that is, difficulty in forming a thin and uniform film on the surface of a base material because it is likely to be influenced by whether or not the atmospheric heating temperature is uniform and provide a formation method of a thin and uniform copper film on the surface of a substrate by using copper formate which is stable and easy in handling.

The present inventors proceeded with an investigation with a view to overcoming the above-described problem. As a result, it was found that a thin and uniform copper film can be formed on the surface of a substrate by spraying an aqueous solution of copper formate to the surface of a substrate heated to a certain temperature in a nitrogen atmosphere and simultaneously carrying out, under the certain temperature, evaporation of water in the resulting mist and thermal decomposition of copper formate without using a catalyst.

It was however elucidated that an oxide film appeared on the surface of the copper film formed on the surface of the substrate or copper formate remained undecomposed on the surface of the substrate and they prevented stable formation of a copper film with good quality.

The present inventors have therefore investigated, thinking that if the oxide film which has appeared on the surface of the copper film formed on the surface of the substrate or the undecomposed residue of copper formate on the surface of the substrate can be reduced with a reducing agent, the copper film thus formed can be made as pure as possible, leading to the completion of the invention.

In view of the above, according to the invention, there is provided a copper film forming method including the steps of:

spraying a copper formate solution including a copper foramate and a solvent which is evaporated at a certain temperature on a surface of the substrate;

spraying a reducing agent solution including a reducing agent for reducing a copper oxide or undecomposed copper formate on the surface of the substrate to the surface of the substrate,

wherein the spraying steps are performed while heating the substrate to the certain temperature and

the substrate is placed in an inert gas which is inert at the certain temperature.

According to another aspect of the invention, it is adaptable that the reducing agent solution is sprayed after spraying the copper formate solution.

According to another aspect of the invention, it is adaptable that the reducing agent contains an ammonium formate or a formic acid.

According to another aspect of the invention, it is adaptable that the reducing agent contains a solvent which is evaporated at the certain temperature;

According to another aspect of the invention, it is adaptable that the step of spraying the copper formate solution and the step of spraying the reducing agent solution is performed alternately.

According to another aspect of the invention, it is adaptable that the copper formate is thermally decomposed without using a catalyst.

According to another aspect of the invention, it is adaptable that the inert gas is a nitrogen gas.

According to another aspect of the invention, it is adaptable that the certain temperature is ranging from 130° C. to 200° C.

According to another aspect of the invention, it is adaptable that the step of spraying the copper formate solution is performed intermittently.

According to another aspect of the invention, it is adaptable that the step of spraying the copper formate solution is performed after the step of spraying the reducing agent solution.

According to still another aspect of the invention, there is provided a manufacturing method of a multi-layer wiring substrate which includes:

a semiconductor layer;

a plurality of insulation layer;

a plurality of wiring layer which is made of copper and provided on the respective insulation layers;

vias electrically connecting the respective wiring layers, the manufacturing method including:

step of forming a (n)th insulating layer on a (n)th wiring layer;

step of forming a via on the (n)th insulation layer;

step of performing a desmear treatment on the via;

a first reducing agent spraying step of spraying a reducing agent solvent on the via;

a copper formate spraying step of spraying a copper formate solution which includes a copper formate and solvent evaporated at a certain temperature, on the (n)th insulating layer and the via; and

a second reducing agent spraying step of spraying the reducing agent solution on the (n)th insulation layer and the via,

wherein the “n” is a natural number,

the spraying steps are performed while heating the insulation layer to the certain temperature, and

the insulation layer is placed in an inert gas which is inert at the certain temperature.

According to still another aspect of the invention, it is adaptable that the second reducing agent spraying step is performed after the copper formate spraying step.

According to still another aspect of the invention, it is adaptable that the reducing agent contains an ammonium formate or a formic acid.

According to still another aspect of the invention, it is adaptable that the reducing agent solution includes a solvent which is evaporated at the certain temperature.

According to still another aspect of the invention, it is adaptable that the copper formate spraying step and the second reducing agent spraying steps are performed alternately.

According to still another aspect of the invention, it is adaptable that the copper formate is decomposed without using a catalyst.

According to still another aspect of the invention, it is adaptable that the inert gas is a nitrogen gas.

According to still another aspect of the invention, it is adaptable that the certain temperature is ranging from 130° C. to 200° C.

According to still another aspect of the invention, it is adaptable that the copper formate spraying step is performed intermittently.

In the invention, a copper film which is nearly a pure copper film can be obtained stably by forming a thin copper film on a surface of a substrate and then spraying a reducing agent solution thereon.

As the reducing agent, ammonium formate or formic acid can be used. As the reducing agent solution, by using a reducing agent solution, which is obtained by adding a solution of such a reducing agent to a solvent which evaporates at the temperature of the heated substrate, facilitates treatment of the solvent after use.

By spraying a copper formate solution and the reducing agent solution alternately to the substrate, a copper film which is close to a pure copper film as much as possible and having a desired thickness can be obtained without leaving copper oxide in the copper film.

In the invention, a rise in the film formation cost which will otherwise occur by the use of an expensive catalyst can be suppressed by carrying out thermal decomposition of copper formate without using a catalyst. In addition, unevenness of a copper film which occurs, depending on the dispersion state of the catalyst on the surface of a base material can be prevented so that a uniform copper film can be formed.

As the inert gas in the atmosphere in which such a copper formate solution and reducing agent solution are sprayed, a nitrogen gas is most economical.

Moreover, even if a resin substrate is used as the substrate, thermal damage to the resin substrate can be prevented by adjusting the temperature of the heated substrate to from 130 to 200° C.

Further, a reduction in the temperature of the substrate during spraying of the copper formate solution can be minimized by intermittently spraying the copper formate solution.

The copper film forming method according to the invention enables thermal decomposition of copper formate without using a catalyst and formation of a uniform and thin copper film on a surface of a substrate. Details of the reason for it are not clear, but can be presumed as follows:

By heating the substrate to a certain temperature, the atmosphere, in which the substrate is placed, is also heated. A mist obtained by spraying the copper formate solution into the heating atmosphere floats in the heating atmosphere and attaches uniformly, as a thin film, onto the surface of the substrate while being heated by the heating atmosphere and evaporating the solvent.

From such a mist of the copper formate solution floating in the heating atmosphere, copper formate separates out as a result of evaporation of the solvent during floating. Moreover, a portion of the copper formate is decomposed into copper or a precursor thereof and attaches to the surface of the substrate.

Thus, since the mist of the copper formate solution attaches onto the surface of the substrate as a thin film while evaporating the solvent and copper or precursor thereof also attaches to the surface of the substrate, the forming method of the invention is capable of minimizing the influence of a thermal decomposition gas on copper formate compared with a process of directly applying a copper formate solution onto the surface of a substrate to form a copper film and thereby forming a uniform and thin copper film on a predetermined surface of the substrate.

However, an oxide film may be formed or undecomposed copper formate may remain on the surface of the copper film formed on the surface of the substrate, though it depends on the film formation conditions.

For example, use of a copper formate solution obtained by dissolving copper formate in a water-containing solvent facilitates formation of an oxide film on the surface of a thin copper film formed on the substrate. Such a phenomenon is presumed to occur because water in a mist composed of the aqueous copper formate solution does not evaporate fully during floating and water vapor formed by the evaporation on the surface of the substrate reacts with the copper film which has been formed already on the surface of the substrate.

When the temperature of the heated substrate is decreased in order to prevent a quality change or deterioration of a resin constituting a resin substrate to be used as the substrate or when the temperature of the heated substrate becomes uneven, undecomposed copper formate may remain on some positions of the surface of the substrate.

In the invention, however, the oxide film which has appeared on the surface of the copper film formed on the substrate or undecomposed copper formate which has remained on the surface of the substrate is reduced with a reducing agent in the solution of the reducing agent so that a nearly pure copper film can be formed stably on the surface of the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating an apparatus for performing the copper film forming method according to the invention;

FIG. 2 is a schematic view illustrating a principle of forming a thin copper film by the copper film forming method according to the invention;

FIGS. 3A to 3D are explanatory views illustrating a recessed substrate over which a thin copper layer is formed by the copper film forming method according to the invention;

FIG. 4 is a sectional view of a multi-layer wiring substrate of the invention;

FIG. 5 is a view explaining a manufacturing method of the multi-layer wiring substrate of the invention;

FIG. 6 is a view explaining a manufacturing method of the multi-layer wiring substrate of the invention;

FIG. 7 is a view explaining a manufacturing method of the multi-layer wiring substrate of the invention;

FIG. 8 is a view explaining a manufacturing method of the multi-layer wiring substrate of the invention;

FIG. 9 is a view explaining a manufacturing method of the multi-layer wiring substrate of the invention; and

FIG. 10 is a view explaining a manufacturing method of the multi-layer wiring substrate of the invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE PRESENT INVENTION

As a substrate, on which a copper film is formed by a forming method of the invention, a substrate which is employed for semiconductor devices or wiring substrates can be used. A substrate made of resin such as epoxy resin or a substrate made of inorganic material such as ceramic also can be used.

Such a substrate is placed in a box 12 having a nitrogen supply port 14 on the lower side of the box, and, an exhaust gas outlet 16, from which gases such as nitrogen gas and thermal decomposition gas are discharged, on the upper side of the box. An interior of the box 12 is filled with the nitrogen gas supplied from the nitrogen supply port 14 and an atmosphere in the box 12 is made inert.

The box 12 further has a heater block 18 therein and the substrate 10 is placed on the heater block 18 and heated to a certain temperature. This temperature is adjusted to enable to keep the inert state of a nitrogen gas. Specifically, the heating temperature of the heater block 18 is preferably adjusted so that the temperature of the substrate 10 falls within a range of from 130 to 200° C.

Toward one side of the substrate 10 heated to the certain temperature, a copper formate solution obtained by dissolving copper formate in a solvent which evaporates at the certain temperature of the substrate 10 is sprayed from a spray nozzle 20. The spray nozzle 20 is supplied with the copper formate solution via a valve 26 and a pipe 24 from a copper formate solution tank 22 disposed outside the box 12.

The spray nozzle 20 is supplied with the reducing agent solution via a valve 40 and the pipe 24 from a reducing agent solution tank 28 disposed outside the box 12.

As the copper formate solution stored in the copper formate solution tank 22, a copper formate solution obtained by dissolving copper formate in a solvent which evaporates at the temperature of the heated substrate 10 is used. As the solvent, water or aqueous ammonia which can easily dissolve copper formate therein and requires only simple treatment can be used preferably. As the copper formate solution, a copper formate solution obtained by adding aqueous ammonia having copper formate dissolved therein to ethyl alcohol is especially preferred.

As the copper formate, copper formate tetrahydrate can be used preferably from the viewpoint of easy availability, stability at room temperature, and high solubility in water or aqueous ammonia.

Spraying of the copper formate solution from the spray nozzle 20 is preferably carried out intermittently so as to keep the temperature of the substrate 10 as constant as possible. Continuous spraying of the copper formate solution from the spray nozzle 20 to the substrate 10 is likely to reduce the temperature of the substrate 10 due to evaporation of the solvent from the sprayed mist.

When the mist of the copper formate solution sprayed from the spray nozzle 20 to the substrate 10 is heated by the heated atmospheric gas in the box 12 and the heated substrate 10, the solvent is evaporated from the mist and copper formate thus precipitated is thermally decomposed without using a catalyst. As a result, a thin copper film is formed on one side of the substrate 10.

The copper formate solution sprayed from the spray nozzle 20 is presumed to follow various routes as illustrated in FIG. 2.

For example, a portion of the mist of the copper formate solution sprayed from the spray nozzle 20 reaches on one side of the substrate 10 while evaporating the solvent due to the heated atmospheric gas in the box 12. The solvent is evaporated completely on the substrate 10 and copper formate is precipitated. The copper formate thus precipitated is thermally decomposed into the corresponding precursor and then decomposed into copper due to the heated substrate 10.

With regard to another portion of the mist of the copper formate solution, the solvent is evaporated therefrom completely during floating by the heated atmospheric gas in the box 12, and the copper formate thus precipitated attaches onto the one side of the substrate 10, is thermally decomposed into the corresponding precursor and then decomposed into copper by the temperature of the heated substrate 10.

With regard to a further portion of the mist of the copper formate solution, the solvent is evaporated therefrom completely during floating by the atmospheric temperature in the box 12, and the copper formate thus precipitated is thermally decomposed into the corresponding precursor and attaches onto the one side of the substrate 10, and then is thermally decomposed into copper by the temperature of the heated substrate 10.

Thus, copper attached to the one side of the substrate 10 forms a thin copper film on the one side of the substrate 10. The copper film thus formed has a film thickness adjusted to preferably not greater than 1 μm.

Since copper formate is readily soluble in water or aqueous ammonia, a copper formate solution obtained by dissolving copper formate in a water-containing solvent is used as the copper formate solution to be sprayed from the spray nozzle 20. An oxide film composed of black copper oxide is sometimes formed on the surface of the copper film formed on one side of the substrate 10 by spraying such a copper formate solution. Compared with a pure copper film, the copper film having on the surface thereof such an oxide film is inferior in electrical properties such as sheet resistance.

The following is a reason why an oxide film is formed on the surface of the copper film formed on one side of the substrate 10.

Specifically, since copper formate is readily soluble in water or aqueous ammonia, a copper formate solution obtained by dissolving copper formate in a water-containing solvent is used. It is therefore presumed that water in the mist composed of the aqueous solution of copper formate cannot evaporate completely during floating and water vapor formed on the surface of the substrate by the evaporation of remaining water reacts with the copper film which has been formed already on the surface of the substrate.

When the temperature of the heated substrate 10 is decreased in order to prevent a quality change or deterioration of the resin substrate used as the substrate 10, or the temperature of the heated substrate 10 becomes uneven, undecomposed copper formate remains partially on one side of the substrate 10 and deteriorates the quality of the copper film thus formed.

In the invention, on the other hand, a reducing agent solution in the reducing agent solution tank 28 is sprayed to the oxide film formed on the surface of the copper film or copper formate remaining on one side of the substrate 10, thereby reducing copper oxide into copper with the reducing agent.

As such a reducing agent, ammonium formate or formic acid can be used. Ammonium formate having no toxicity is especially preferred. Of these reducing agents, formic acid is liquid at room temperature and therefore does not need conversion into a solution. On the other hand, ammonium formate in solid form at room temperature is preferably converted into a solution by dissolving it in a solvent which evaporate at the temperature of the heated substrate 10. As the solvent, water or aqueous ammonia is preferred because it can readily dissolve ammonium formate therein and in addition, can be treated easily. Use of a reducing agent solution obtained by adding aqueous ammonia having ammonium formate dissolved therein to ethyl alcohol is especially preferred.

Spraying of such a reducing agent solution from the spray nozzle 20 is preferably performed intermittently to keep the temperature of the substrate as constant as possible. Continuous spraying of the reducing agent solution to the substrate 10 from the spray nozzle 20 is likely to reduce the temperature of the substrate 10 due to evaporation of the solvent from the sprayed mist.

By spraying the copper formate solution and the reducing agent solution alternately on one side of the substrate 10 from the spray nozzle 20, a copper film as pure as possible and having a desired thickness can be formed on one side of the substrate 10.

Alternate spraying of the copper formate solution and the reducing agent solution to one side of the substrate 10 from the spray nozzle 20 can be achieved by alternately opening or closing the valve 26 of the copper formate solution tank 22 and the valve 40 of the reducing agent solution tank 28 as illustrated in FIG. 1.

The invention enables formation of a copper film which is nearly a pure copper film on the flat surface of the substrate. Even if the surface of the substrate has recesses therein, the copper film may also be formed along the inner wall surface of the recesses.

For example, after formation, in a resin layer 32 formed on one side of the substrate 30 as illustrated in FIG. 3A, of a recess 34 having a bottom surface from which the surface of the substrate is exposed by laser as illustrated in FIG. 3B, a resin residue which has remained on the bottom surface of the recess 34 is removed by etching of the bottom surface of the recess 34. By such etching, a minute undercut portion 34 a is formed on the bottom surface side of the recess 34 as illustrated in FIG. 3C.

The substrate 30 having the recess 34 formed as illustrated in FIG. 3C is placed on the heater block 18 as illustrated in FIG. 1 and the copper formate solution and the reducing agent solution are alternately sprayed to the substrate from the spray nozzle 20. As a result, a thin copper film 36 can be formed along the inner wall surface of the recess 34 including the inner wall surface of the undercut portion 34 a as illustrated in FIG. 3D.

When sputtering is employed for the formation of a copper film in the recess 34 having the undercut portion 34 a as illustrated in FIG. 3C, on the other hand, the copper film cannot be formed along the inner wall surface of the undercut portion 34 a.

In the above description, the atmosphere in the box 12 is filled with a nitrogen gas, but it may be filled with an inert gas belonging to the “0” group of the periodic table such as argon gas.

Moreover, the copper formate solution and the reducing agent solution are sprayed from one spray nozzle 20, but spray nozzles exclusively used for the copper formate solution and the reducing agent solution may be disposed, respectively. Use of the respective spray nozzles exclusively used for these solutions facilitates alternate spraying of the copper formate solution and the reducing agent solution.

In the above description, the spraying of the reducing agent solution from the spray nozzle 20 is performed after formation of a copper film on one side of the substrate 10. Alternatively, a mixture of the copper formate solution and the reducing agent solution may be sprayed from the spray nozzle 20, or the copper formate solution and the reducing agent solution may be sprayed simultaneously from the spray nozzles exclusively used for them.

EXAMPLE 1

A copper film was formed on one side of a substrate 10 made of soda-lime glass by using an apparatus as illustrated in FIG. 1.

The other side of the substrate 10 was placed on the heater block 18 in the box 12 and the substrate 10 was heated so that the one side of the substrate 10 becomes 160° C. by controlling the heater in the heater block 18.

A nitrogen gas was supplied in the box 12 at a rate of 60 liter/min from the nitrogen supply port 14 disposed on the lower side of the box 12, while a nitrogen gas containing a decomposition gas was discharged from the exhaust gas outlet 16 disposed on the upper side of the box 12.

A copper formate solution stored in the copper formate solution tank 22 was intermittently sprayed to the one side of the substrate 10 from the spray nozzle 20 placed at 40 cm height from the one side of the substrate. The copper formate solution was obtained by mixing, with ethanol, a solution obtained by dissolving copper formate tetrahydrate in aqueous ammonia. In that case, amounts of the aqueous ammonia and ethanol were 10 ml and 40 ml, respectively, based on 0.1 g of copper formate tetrahydrate.

On the one side of the substrate 10 to which the copper formate solution was sprayed 100 times, a copper film was formed. The copper film had, on the surface thereof, an oxide film composed of black copper oxide.

The reducing agent solution stored in the reducing agent solution tank 28 was sprayed intermittently from the spray nozzle 20 to the copper film having on the surface thereof such an oxide film. The reducing agent solution was obtained by adding a solution obtained by dissolving ammonium formate in aqueous ammonia to ethanol. In that case, amounts of aqueous ammonia and ethanol were 3 ml and 14 ml, respectively, based on 0.11 g of ammonium formate.

On the one side of the substrate 10 to which the reducing agent solution was sprayed 30 times, the black oxide film disappeared and a copper film with a copper color was formed.

The sheet resistance of the copper film formed on the one side of the substrate 10 was measured, resulting in from 0.2 to 1Ω.

COMPARATIVE EXAMPLE 1

In Example 1, the sheet resistance of a copper film having on the surface thereof an oxide film composed of black copper oxide was measured without spraying the reducing agent solution to the one side of the substrate 10, resulting in from 80 to 350 kΩ.

EXAMPLE 2

In a similar manner to Example 1 except that a resin substrate was used instead of the substrate 10 made of soda-lime glass, a copper film was formed on one side of the resin substrate. The copper film thus formed had a copper color and it had a sheet resistance of 1Ω.

EXAMPLE 3

In a similar manner to Example 1 except that the substrate 10 made of a soda-lime glass was replaced by the substrate 30 in which the recess 34 with the undercut portion 34 a was formed as illustrated in FIG. 3( c), a copper film with a copper color was formed on the side of the substrate 30 having the recess 34 formed therein.

As illustrated in FIG. 3( d), the copper film 36 was formed also along the inner wall surface of the undercut portion 34 a of the recess 34 of the substrate 30.

EXAMPLE 4

In a similar manner to Example 1 except that ammonium formate was replaced by formic acid and formic acid was used in an amount of 0.073 ml, a copper film was formed on one side of the substrate 10. The copper film thus formed had a copper color and had a sheet resistance of from 0.3 to 3.4Ω.

EXAMPLE 5

In a similar manner to Example 1 except that a solution obtained by mixing a copper formate solution and a reducing agent solution and stored in a tank 22 was sprayed 100 times to one side of the substrate 10 from the spray nozzle 20, a copper film was formed on the one side of the substrate 10. The copper film thus formed had a sheet resistance of from 420 to 41 kΩ. The sheet resistance of the resulting copper film is improved over that (from 80 to 350 kΩ) of the copper film (Comparative Example 1) formed by spraying only a copper formate solution on the one side of the substrate 10.

Next, an example of manufacturing a multi-layer wiring substrate by using the above described copper film forming method will be explained.

With reference to FIG. 4, a multi-layer wiring substrate 100 generally includes an insulating layer 110, a plurality of insulation layer 120, a plurality of wiring layer provided on the respective insulation layer 120, and vias 140 electrically connecting the wiring layers each other.

The manufacturing method of the multi-layer wiring substrate 100 according to the present invention includes:

a step of forming a copper film on a (n)th insulation layer 120;

a step of forming a (n)th wiring layer 130 by etching the copper film;

a step of forming a (n+1)th insulation layer 120 on the (n)th wiring layer 130 (see FIG. 5);

a step of forming a hole 145 by irradiating a laser beam on the (n+1)th insulation layer (see FIG. 6);

a step of performing a desmear treatment so as to remove a smear 150 which is melt and remained (n+1)th insulation layer 120 by the laser beam; and

a step of applying copper on the hole 145 and the (n+1)th insulation layer 120.

These steps are repeated and desired numbers of insulation layers 120 and wiring layers 130 are formed. Further, the hole 145 is filled with the copper and thus the via 140 is formed. Here, the (n) is a natural number.

The desmear treatment is performed by immerging the substrate in manganese peroxide. Further, it is adaptable to perform soft etching after the desmear treatment for surely removing the residual smear and copper oxide.

When applying the above described copper forming method to the above multi-layer wiring substrate 100, following problem can be considered.

After performing the desmear and soft etching treatment, a clean copper surface is exposed from a bottom of the hole 145. When heating the substrate for applying the copper on the clean copper surface, the exposed copper surface get oxidized and a copper oxide 131 is formed on the bottom of the hole 145. If this copper oxide 131 is formed, which exhibits non-electric conducting property, the reliability of electric connection between the wiring layers 130, 130 through the via 140 deteriorates. It should be noted that the copper oxide 131 may be formed in a drying step performed after wet etching process which is performed after the desmear treatment.

In view of the above problems, according to the present invention, when manufacturing the multi-layer wiring substrate by using the copper film forming method, as shown in FIG. 7, the substrate is placed in the inert gas; and spraying a reducing agent such as a formic acid or ammonium formate to the substrate while heating the substrate to a certain temperature or after heating the substrate (a first reducing agent spraying step). By spraying the reducing agent, the copper oxide 131 is reduced and a clean copper surface 132 is obtained. This first reducing agent spraying step is performed while heating the substrate (including the semiconductor layer 110, the insulation layer 120 and the wiring layer 130) to the certain temperature.

Next, a copper film 130′ is formed on the insulation layer 120 by the above described copper film forming method. That is, as shown in FIG. 8, the substrate is heated to the certain temperature a copper formate solution and the reducing agent solution are sprayed on the clean copper surface 132 from a nozzle 20, thereby the copper film 130′ as shown in FIG. 9 is formed.

It is preferable that in this spraying step, the copper formate solution and the reducing agent solution are sprayed alternately. This copper formate solution spraying step is also performed by heating the substrate (including the semiconductor layer 110, the insulation layer 120 and the wiring layer 130) to the certain temperature. By doing so, the solvent in the copper formate solution is evaporated, or the copper formate is decomposed and only the copper is separated out, while the mist of the copper formate solution moving in the inert gas.

After forming the copper film 130′, as shown in FIG. 10, the via 140 is formed by filling the copper in the hole 145 by an electrolytic plating method in which the copper film 130′ is used as an electrode. Further, it is adaptable to form the copper film 130 by applying the copper further on the copper film 130′ formed on the insulation layer 120.

Thus, according to the present invention, following manufacturing method of the multi-layer wiring substrate is obtained. The manufacturing method of a multi-layer wiring substrate 100 which includes: a semiconductor layer 110; a plurality of insulation layer 120; a plurality of wiring layer 130 which is made of copper and provided on the respective insulation layers 120; vias 140 electrically connecting the respective wiring layers 130, the manufacturing method including: step of forming a (n)th insulating layer 120 on a (n)th wiring layer 130; step of forming a hole 145 on the (n)th insulation layer; step of performing a desmear treatment on the hole 145; a first reducing agent spraying step of spraying a reducing agent solvent on the hole 145; a copper formate spraying step of spraying a copper formate solution which includes a copper formate and solvent evaporated at a certain temperature, on the (n)th insulating layer 120 and the hole 145; and a second reducing agent spraying step of spraying the reducing agent solution on the (n)th insulation layer 120 and the hole 145. The “n” is a natural number, the spraying steps are performed while heating the insulation layer 120 to the certain temperature, and the insulation layer 120 is placed in an inert gas which is inert at the certain temperature.

According to the manufacturing method of the multi-layer wiring substrate of the present invention, the copper film can be formed on the hole 145 to form the via 140 without using a wet process such as an electroless deposition. Thus, it is not necessary to handle harmful waste liquid due to the wet process and environment load can be reduced.

Further, according to the present invention, the copper film can be formed by spraying the copper formate solution immediately after reducing the copper oxide 131. Thus, the multi-layer wiring substrate 100 having high reliability and high electric conducting property can be provided.

While the invention has been described in connection with the exemplary embodiments, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the present invention, and it is aimed, therefore, to cover in the appended claim all such changes and modifications as fall within the true spirit and scope of the present invention. 

1. A copper film forming method, comprising the steps of: spraying a copper formate solution comprising a copper foramate and a solvent which is evaporated at a certain temperature on a surface of the substrate; spraying a reducing agent solution comprising a reducing agent for reducing a copper oxide or undecomposed copper formate on the surface of the substrate to the surface of the substrate, wherein the spraying steps are performed while heating the substrate to the certain temperature and the substrate is placed in an inert gas which is inert at the certain temperature.
 2. The copper film forming method according to claim 1, wherein the reducing agent solution is sprayed after spraying the copper formate solution.
 3. The copper film forming method according to claim 1, wherein the reducing agent contains an ammonium formate or a formic acid.
 4. The copper film forming method according to claim 1, wherein the reducing agent contains a solvent which is evaporated at the certain temperature;
 5. The copper film forming method according to claim 1, wherein the step of spraying the copper formate solution and the step of spraying the reducing agent solution is performed alternately.
 6. The copper film forming method according to claim 1, wherein the copper formate is thermally decomposed without using a catalyst.
 7. The copper film forming method according to claim 1, wherein the inert gas is a nitrogen gas.
 8. The copper film forming method according to claim 1, wherein the certain temperature is ranging from 130° C. to 200° C.
 9. The copper film forming method according to claim 1, wherein the step of spraying the copper formate solution is performed intermittently.
 10. A manufacturing method of a multi-layer wiring substrate which comprises: a semiconductor layer; a plurality of insulation layer; a plurality of wiring layer which is made of copper and provided on the respective insulation layers; vias electrically connecting the respective wiring layers, the manufacturing method comprising: step of forming a (n)th insulating layer on a (n)th wiring layer; step of forming a via on the (n)th insulation layer; step of performing a desmear treatment on the via; a first reducing agent spraying step of spraying a reducing agent solvent on the via; a copper formate spraying step of spraying a copper formate solution which comprises a copper formate and solvent evaporated at a certain temperature, on the (n)th insulating layer and the via; and a second reducing agent spraying step of spraying the reducing agent solution on the (n)th insulation layer and the via, wherein the “n” is a natural number, the spraying steps are performed while heating the insulation layer to the certain temperature, and the insulation layer is placed in an inert gas which is inert at the certain temperature.
 11. The manufacturing method of the multi-layer wiring substrate as set forth in claim 10, wherein the second reducing agent spraying step is performed after the copper formate spraying step.
 12. The manufacturing method of the multi-layer wiring substrate as set forth in claim 10, wherein the reducing agent contains an ammonium formate or a formic acid.
 13. The manufacturing method of the multi-layer wiring substrate as set forth in claim 10, wherein the reducing agent solution comprises a solvent which is evaporated at the certain temperature.
 14. The manufacturing method of the multi-layer wiring substrate as set forth in claim 10, the copper formate spraying step and the second reducing agent spraying steps are performed alternately.
 15. The manufacturing method of the multi-layer wiring substrate as set forth in claim 10, wherein the copper formate spraying step is performed intermittently. 